Today , SpaceX is focusing its efforts on commercial spaceflights to the International Space Station, the first of which will hopefully take place in December, according to CEO Elon Musk. But in the coming years, Musk has plans for commercial journeys—and settlements—on places like the Moon and Mars.

"Ultimately, the thing that is super important in the grand scale of history is—are we on a path to becoming a multi-planet species or not? If we’re not, that’s not a very bright future. We’ll just be hanging out on Earth until some eventual calamity claims us," Musk said.

First on his to-do list would be a vehicle that's capable of delivering substantial mass to Mars and then returning to Earth. The company's planned Falcon Heavy rocket, the plans for which were unveiled in April, could conceivably carry 12 to 15 metric tons, but "I think you'll probably want a vehicle that can deliver something on the order of 50 metric tons … in a fully reusable manner," Musk said.

The Falcon Heavy, which will be the world's largest rocket, will have its inaugural flight in late 2012.When asked about using nuclear propulsion on Mars, Musk was skeptical that people would approve.

"I think it's going to be tough to convince the public that we should launch large reactors into space" and possibly spread uranium on Earth, he said. It might be possible to build a reactor on Mars or the Moon, but people usually forget how heavy reactors are and that many of them usually have a source of water nearby to drive the steam turbine. If fusion were to become a reality, "that would be very cool," Musk said, but solar panels are also an option.

At this point, however, the main goal is to actually get to Mars. As soon as a base is established, there will be a bigger incentive to improve transportation, he said, pointing to ships that first traveled to the American colonies.

"Before the U.S. colonies were established, there was no forcing function for improving trips across the Atlantic. But when there was, there was a need to make those ships better and better," Musk said.

Cost, of course, is also a factor. At this point, the cost per pound for the Falcon Heavy is about $1,000, but to make this a sustainable effort, the cost per pound would probably need to be well under $100, probably closer to $50, he said. Making the Falcon Heavy totally reusable would help drive down costs.

Recent research suggests that conditions on Mars are capable of supporting dormant bacteria, known as endospores. This raises concern about future attempts to detect Martian life forms because endospores originating on Earth could potentially hitch a ride to Mars and survive on its surface.

Soil on Mars is thought to be rich in oxidising chemicals that are known to destroy life. The high levels of ultraviolet radiation on the surface of the planet make it unlikely that any organism could survive. Ronald Crawford and colleagues from the University of Idaho have investigated whether bacterial endospores can exist in Mars’s hostile environment.

Endospores are a survival form of bacteria, formed when they find themselves in an unfavourable environment, and are perhaps the most resilient life form on Earth. They are resistant to extreme temperatures, most disinfectants, radiation, drying, and can survive for thousands of years in this dormant state. There is even evidence that they can survive in the vacuum of space. Given the possibility of endospores hitching a lift on spacecraft bound for Mars, Ronald Crawford and his colleagues investigated whether endospores could survive in a simulated Martian environment.

Martian soil was created by mixing dry sand containing endospores with ferrate. The soil was then left at –20 oC and exposed to high levels of UV light for six weeks. These conditions were designed to simulate the dry, cold, oxidizing environment found on Mars. Subsequent analysis of the soil showed that endospores were still alive below a depth of 5mm, suggesting that life is possible in these hostile conditions.

The authors speculate, “that if entities resembling bacterial endospores were produced at some point by life forms on Mars, they might still be present and viable, given appropriate germination conditions.”

Although the researchers have not found direct evidence for life on Mars their research does throw up a potential problem with future space missions. The survival of endospores in such adverse conditions raises the possibility that bacterial endospores could travel to Mars on the surface of spacecraft and survive on Martian soil. This could seriously compromise future efforts to establish whether there is, or has been life on Mars, as it would be difficult for researchers to know whether any endospores found originated from Earth or Mars.

While this work establishes that bacterial endospores can survive exposure to the conditions probably found on Mars, it should be noted that it was not possible to test whether their simulated Martian environment would kill endospores over a geological timescale.

It's a concern future commercial probes such as the Space X Mars venture will have to address.